Silane is a versatile compound that has many industrial uses. In the semiconductor industry, silane may be utilized for deposition of an epitaxial silicon layer on semiconductor wafers and for production of polycrystalline silicon. Polycrystalline silicon is a vital raw material used to produce many commercial products including, for example, integrated circuits and photovoltaic (i.e., solar) cells that may be produced by thermal decomposition of silane onto silicon particles in a fluidized bed reactor.
Silane may be produced by reacting silicon tetrafluoride with an alkali or alkaline earth metal aluminum hydride such as sodium aluminum tetrahydride as disclosed in U.S. Pat. No. 4,632,816, which is incorporated herein by reference for all relevant and consistent purposes. Silane may alternatively be produced by the so-called “Union Carbide Process” in which metallurgical-grade silicon is reacted with hydrogen and silicon tetrachloride to produce trichlorosilane as described by Müller et al. in “Development and Economic Evaluation of a Reactive Distillation Process for Silane Production,” Distillation and Adsorption: Integrated Processes, 2002, which is incorporated herein by reference for all relevant and consistent purposes. The trichlorosilane is subsequently taken through a series of disproportionation and distillation steps to produce a silane end-product.
After silane is produced, it is conventionally taken through a purification process to remove impurities prior to use (e.g., prior to epitaxial layer production or polycrystalline silicon production). Examples of impurities that may be present in the silane-containing process streams include, for example, nitrogen, methane, hydrogen, ethane, ethylene, ethyl-silane, diethyl silane, toluene, dimethoxyethane and combinations of these impurities. Examples of such purification processes include those disclosed in U.S. Pat. Nos. 5,206,004; 4,554,141 and 5,211,931, each of which is incorporated herein by reference for all relevant and consistent purposes. Such conventional processes may adequately purify silane-containing process streams; however, they are characterized by relatively high rates of unrecoverable silane.
A continuing need therefore exists for processes for purifying silane-containing process streams that achieve relatively high silane purity and a relatively high rate of silane recovery. A need also exists for systems for such processes.